Brocchi’s Cluster, Collinder 399

Brocchi’s Cluster; Al Sufi’s Cluster; The Coathanger Cluster

This cluster of about 40 stars was discovered by Al Sufi and described in 964

AD. It was independently rediscovered by Hodierna. Messier, the Herschels and

the NGC did not assign it a number, probably because of the cluster’s size:

Even at moderate power, it doesn’t match in one field of view, and is best

seen in a good pair of binoculars. Also, its appearance suggests it might be

an asterism only.

In 1970, investigations of Hall and Landingham revealed that perhaps only 6

of the brighter stars and none of the fainter ones appear to have a common

proper motion, thus indicating that they may form a cluster. In the late

1980s, Pavlovskaya and Filipova were looking for common proper motion of open

clusters, and found that the Coathanger was sharing spacial motion with about

10 other clusters, including

NGC 6633, 6709, 6882, 6885, and

Collinder 399 was found to approach us at 18 km/sec.

(info from Bernd Nies)

Brian Skiff of Lowell Observatory has investigated astrometrical data of the

stars counted to Collinder 399 acquired by ESA’s Hipparcos satellite, and

that this object may be an asterism instead of a cluster

(Sky & Telescope).

Last Modification: 29 Mar 1998, 13:30 MET